Minimally invasive surgical procedures continue to experience explosive growth. Such procedures are often preferred to other more invasive procedures in that incisions are kept to a minimum size and thus such procedures facilitate shorter hospital stays and lower costs. For example, with laparoscopic surgery, a patient can return to normal activity within about one week, whereas with procedures where a large incision is made, about a month for full recovery may be required. It should be understood that hereinafter and in the claims, whenever the term “laparoscopic” is employed, similar procedures such as pelviscopic, arthroscopic, thoroscopic, and other procedures where small incisions of the foregoing type are made are also encompassed by this term. FIG. 1 described herein represents the general concept behind an electrosurgical apparatus and how it is used in a surgical setting. Referring to FIG. 1, there is illustrated an electrosurgical laparoscopic surgical system 100 including an electrosurgical tool 104 which is conventionally used to perform various surgical procedures such as ablation, incision, cauterization, etc. As is known in the laparoscopic field, a portion of the tool 104 is provided through a small incision in a patient's skin into, for example, the peritoneal cavity. The electrosurgical tool is typically provided with an active electrode probe 106 which includes an electrode and an insulative coating thereon. The tip of the probe 106 may be of different conventional shapes such as needle-shape, hook-shape, spatula-shape, graspers, scissors, etc. and serve various conventional functions such as suction, coagulation, irrigation, cutting, etc. Current is supplied to the electrosurgical tool by a generator or other electrosurgical unit 102. In order to prevent burns or other trauma to a patient 120 due to the flow of electrical current through uncontrolled paths, a return electrode 110 is placed on the patient. The return electrode 110 is then connected to the electrosurgical unit 102 via conductors 112 and 114 so that the electrical current is returned to the ESU 102 through a controlled path. While laparoscopic devices have enjoyed much success, several problems continue to present themselves.
First, if the insulation on the active electrode is damaged thereby allowing the active current (possibly in the form of arcing) to pass therethrough directly to the patient's tissue (possibly the bowel or colon), peritonitis may set in within several days. The arcing may occur out of the surgeon's field of view which may extend as little as about 2 centimeters from the tip of the active electrode (or the surgical field). The field of view is typically established by illumination and viewing sources inserted through one or more other trocar sheaths at other incisions.
Out of the field of view, there can be many centimeters of insulated active electrode which extend between the trocar sheath and the field of view. This area which is out of the field of view is potentially dangerous. Here, the insulated active electrode may come into contact with the bowel in procedures where the gall bladder, for example, is removed. If the damaged insulation and thus the attendant arcing were to occur within the field of view, the surgeon normally would immediately observe this and deactivate the generator. However, the damaged insulation can and more probably will occur at a site removed from the field of view and thus the surgeon will not be able to observe the arcing which is occurring at the bowel. Furthermore, due to the repeated insertion of the active electrode probe through the trocar sheath, the insulation thereon can be damaged especially since this accessory is quite often pushed through the trocar sheath rather roughly. Hence, damage to the active electrode insulation is particularly a problem in that the full active current may pass through the area of damaged insulation to the return electrode via an unintended site such as the bowel.
A second problem which can arise with the prior art device of FIG. 1 is caused by a capacitive effect where one electrode of the capacitance is the active electrode and the other electrode of the capacitance is the metallic trocar sheath and the dielectric between these elements is the insulation on the active electrode, as can be seen in FIG. 2B. Current from the active electrode will be capacitively coupled to the trocar sheath and then returned through the body and the return electrode to the generator. If this current becomes concentrated, for example, between the trocar sheath and an organ such as the bowel, the capacitive current can cause a burn to the organ.
A third potential problem occurs if the active electrode contacts another instrument within the peritoneal cavity such as metallic graspers or the like. The above-mentioned capacitive effect also arises in this situation where the first electrode is the active electrode and the second electrode is the metallic graspers or the like. Thus, where the graspers contact a unintended site, injury may occur.
As a first, and effective way to prevent the problems described above from presenting themselves, monitored electrosurgical tools, where a return shield is actively monitored in order to prevent unwanted current from burning or otherwise injuring a patient were developed. Systems of this type are known in the art and are exemplified by U.S. Pat. No. 5,312,401 (“the '401 patent”). The details of the '401 patent are hereby incorporated by reference in its entirety.
FIGS. 2A-3B represent a generalized representation of an AEM (“Active Electrode Monitoring”) system 200 embodied by the '401 patent. This system 200 generally includes an electrosurgical generator 102 connected to a laparoscopic instrument 210 via conductors 212 and 214. The instrument 210 includes a tube assembly 220 whereby the instrument 210 provides electrical current from the generator 102 via an active electrode 215. Interposed between a patient return electrode 108 and the generator 102 is an active monitoring system 202 that monitors for one or more fault conditions in the instrument 210. FIG. 2B shows various details of the construction of the monitored instrument 220, including a metal active conductor 222, a high dielectric insulator 224, a metal shield 226, and a non-conductive outer insulating sheath 228. To render laparoscopic electrosurgical procedures more safe and thus overcome the above-mentioned problems, AEM systems such as those described in the '401 patent provide a tubular, insulated, conductive safety shield which extends at least from the trocar sheath to the field of view (that is, typically within less than two centimeters from the active electrode tip). This provides the protection which is needed with respect to the above-discussed first problem where arcing may occur at an unintended site out of the field of view.
Assuming the insulation on the active electrode 222 is damaged, current will pass through the damaged insulation to the shield and then be returned to the return lead via a low impedance electrical connection between the shield and the return lead of the electrosurgical generator where the impedance should be less than about 20 ohms. A monitor circuit responsive to the shield current preferably deactivates the electrosurgical generator whenever the shield current corresponds to an abnormal condition such as an insulation breakdown. FIGS. 3A and 3B show another representation of the electrosurgical tool 210, including active electrode tip 230. Devices constructed in accordance with the '401 patent have been commercialized by Encision, Inc. of Boulder, Colo.
Despite the success obtained, and increased patient safety realized, by the inventions embodied in the '401 patent, as well as the electrosurgical tools that embody those inventions, there remain certain problems and drawbacks, as well as room for improvement.
These drawbacks include, among other things, the need for highly sophisticated and expensive electronics in addition to the actual surgical tool itself. For example, monitoring circuitry associated with these systems often includes a separate stand-alone monitor that interfaces with the electrosurgical generator. This additional piece of hardware increases total operating cost and represents an additional capital investment for a hospital or physician. Because the monitoring unit must interface with electrosurgical generators made by various manufacturers, compatibility issues may arise with traditional electrosurgical tools and systems. Finally, by requiring a separate piece of hardware, it becomes necessary to convince hospitals, doctors, and service providers to purchase a separate monitoring system for their electrosurgical needs. Modern electrosurgical generators come equipped with their own contact quality monitoring circuitry and it would be beneficial to take advantage of this existing hardware in order to provide a monitored electrosurgical tool that provides increased safety to a patient.
Thus, there is a need for a simpler way to provide a monitored electrosurgical circuit that deactivates the current source of the device when there is a fault condition or other problem. The various aspects of the present invention provide a way to benefit from the increased patient safety associated with monitored electrosurgical instruments while eliminating the above described downsides.